Supplementary catalytic converter heaters or air injection reaction systems may be required to meet future vehicle exhaust emissions regulation for low emission vehicles (LEV) or ultra-low emission vehicles (ULEV). Such pollution control schemes may incorporate an air-moving device to provide air for combustion heating of the converter or to promote thermal oxidation reactions within it. If these systems are periodically deactivated to conserve energy, some sort of air injection valve with a check function must isolate the air pump or blower from hot exhaust gases.
The nature of a reciprocating, internal combustion engine exhaust system complicates the air injection valve design requirements somewhat. The average back pressure 82 will rise with increments in engine speed 84 and load or vehicle speed 86 (see FIG. 3). A sudden throttle maneuver or an after-fire (undesired combustion of a misfired cylinder charge within the exhaust system) can generate transient pressure spikes. Additionally, exhaust pressure 92 during an idle or other low speed, light load conditions 94 will oscillate above and below atmospheric pressure (see FIG. 4). Unless the air injection valve is designed carefully, the negative portions of this characteristic trace could permit the converter to draw in undesirable excess oxygen.
Singular, existing valve conventions have various shortcomings. When open, ball-check, reed, umbrella and other one-way type valves are characterized by an inherent pressure loss. Additionally, back flow sealing capability is dependent on the pressure differential and spring force available when closed. Effective sealing against the aforementioned idling exhaust system pulsations would significantly compromise open position pressure drop. Use of a poppet-type, direct acting solenoid valve is restricted by existing direct current coil technology. The severe underhood temperature and operating voltage extremes are costly design constraints. Moreover, limited stroke potential would necessitate a large orifice and hence a large current-robbing coil. Although a piloted diaphragm-type solenoid valve could operate with a short stroke and small coil, these designs sacrifice response and often impose a parasitic pressure drop to open.
Clouding the issue further, intake manifold vacuum may not be available as the driving force for a diaphragm-assisted valve. Some air induction type pollution control devices may need to be activated prior to or during an engine cranking event. Ultimately, future non-throttling internal combustion engines may have no manifold vacuum at all.